1. Field of the Invention
The present invention relates to the field of computer system networks, particularly to the Carrier Sense Multiple Access with Collision Detection (CSMA/CD) access method. More specifically, the present invention relates to unshielded twisted pair media and valid data detection.
2. Art Background
In a computer system network, computers and data devices are physically connected to each other via a medium connected to the "medium attachment units" of the computers/data devices. Data are transmitted from one computer/data device to another as electrical signals over the connecting medium. Inherent in electrical signal transmission are noises, jitters, fluctuations in amplitude and frequency, etc. Thus, electrical signals that represent valid data must be differentiated from those that are merely noises or invalid data.
Historically, computer system networks are primarily comprised of homogeneous hardware from the same vendor, or compatible hardware from cooperating vendors that are designed to work with each other. Furthermore, the hardware including most of the connecting media typically operated in "protected" environment. Thus, the problem of differentiating electrical signals representing valid data from those that are not is not particularly difficult. They are solved in a variety of manners, and are well known in the art.
Today, with the availability of a full range of competitively priced hardware from different vendors, computer system networks tend to be comprised of heterogeneous hardware from multi-vendors. Additionally, as affordability continues to widen the application of information processing technology, more and more computer system networks, particularly local area networks in the office environments, are connected with twisted pair media and operated without special environmental supports. At the same time, as state-of-the-art technology continues to increase the operating speed of hardwares, the timing within which the differentiation has to be made has gotten shorter and shorter. Thus, the task of differentiating electrical signals representing valid data from those that are not has become more increasingly difficult.
For example, under the IEEE's Twisted-Pair Medium Attachment Unit and Baseband Medium, Type 10Base-T standard (IEEE Standard 802.3i-1990), it is required that:
1. All continuous signals of amplitude less than 6.2 v peak to peak and frequency lower than 2MHz must be rejected.
2. All sign waves of single cycle duration starting with phase 0 or 180 degrees, of amplitude less than 6.2 v peak to peak, and of frequency between 2 and 15MHz must be rejected if the line is idle 4 bits before and after the sinusoid.
3. All signals with peak magnitude lower than 300 mv must be rejected.
4. A 5MHz or 10MHz data or a combination of both with a +/-13.5 nanoseconds of jitter must be accepted as valid data.
5. The data valid detection signal must be synchronized to the internal clock.
6. Valid data must be detected within 400 nanoseconds on the RD+, RD- pair.
7. In case of a regular Manchester encoded packet with 5MHz preamble bits in the beginning, the synchronous valid data signal delay from the beginning of the data packet should not vary by more than 2 bits from packet to packet. The first bit can be 0 or 1 and the very first pulse can be short pulse, i.e. 50 nanoseconds. Also there may or may not be a link pulse (a single sinusold) immediately before the packet.
Thus, it is required to be able to detect valid data from a twist pair medium under the modern computer system network operating environment. In particular, it is required to be able to meet the IEEE standard for detecting valid data from a twist pair medium. As will be disclosed, the present invention provides a method and apparatus for detecting valid data from a twist pair medium which achieves the objects and desired results described above.